The present invention relates to a system for transmitting the power of an engine to front and rear wheels of a four-wheel drive vehicle and more particularly to an arrangement in a transfer device of the system.
Japanese Utility Model Laid open 61-170747 discloses a power transmitting system having a final reduction gear secured to a case of a differential, front axles to which the power of an engine is transmitted from a transmission through the final reduction gear, a transfer shaft disposed in parallel to the front axles, a transfer gear rotatably mounted on the transfer shaft and in mesh with the final reduction gear, a drive bevel gear secured to the transfer shaft and in mesh with a driven bevel gear of a rear drive shaft which is perpendicularly disposed to the transfer shaft, and a coupling device provided on the transfer shaft to connect the transfer gear with the transfer shaft for transmitting the power to the transfer shaft. The coupling device is disposed between the transfer gear and the axis of the rear drive shaft, and the bearings for supporting the transfer shaft are disposed on both ends thereof. Since the rear drive shaft and the differential are disposed near the center line of the body of the vehicle, with respect to the width thereof, the lengths of the right and left front axles are substantially equal to each other, thereby preventing the vehicle from deviating from a course.
In such a device, there is a problem that the transfer shaft is deflected by the centrifugal force and thrust exerted on the drive bevel gear. Thus, engaging surfaces of the bevel gears are obliquely shifted, generating gear noise.
In addition, the transfer shaft is supported at the ends thereof so that a heavy load consisting of the coupling device, transfer gear and drive bevel gear is exerted on the transfer shaft. Furthermore, a space is formed about the bevel gears, so that oil is accumulated therein. Such a structure having an oil accumulation space causes not only lubrication efficiency in the transmission system to deteriorate, but also increases the weight thereof.